State change stabilization in a phase shifter/attenuator circuit

ABSTRACT

An electronic system that includes a digitally selectable phase shifter circuit and an insertion loss fine adjustment circuit such that the system as a whole exhibits little or no change in insertion loss when changing phase state, and/or a digitally selectable attenuator circuit and a phase fine adjustment circuit such that the system as a whole exhibits little or no effect on phase when changing attenuation state. Included are methods for selecting adjustment control words for such circuits.

CROSS REFERENCE TO RELATED APPLICATIONS—CLAIMS OF PRIORITY

The present application is a continuation of U.S. application Ser. No.14/752,353 entitled “State Change Stabilization in a PhaseShifter/Attenuator Circuit”, filed on Jun. 26, 2015, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND (1) Technical Field

This invention relates to electronic circuitry, and more particularly todigitally selectable phase shifter and/or digitally selectableattenuator circuits.

(2) Background

Electronic phase shifter circuits are used to change the transmissionphase angle of a signal, and are commonly used to phase shift radiofrequency (RF) signals. Modern phase shifter circuits may be digitallycontrolled and thus provide a discrete set of phase states that areselected by a binary control word. Some phase shifter circuits alsoinclude a digitally controlled RF signal attenuator circuit thatprovides a discrete set of attenuation states that are selected by abinary control word.

FIG. 1 is a block diagram of a prior art electronic system 100 thatincludes a selectable phase shifter circuit 102 coupled to a selectableattenuator circuit 104 and an input/output interface 106. The selectablephase shifter circuit 102 and the selectable attenuator circuit 104modify an RF input signal, RF_In, to generate an RF output signal,RF_Out. The illustrated embodiment may be useful, for example, in radarsystems, phased array antenna systems, and cellular radio transmittersand receivers.

The input/output interface 106 allows user selection of particular phasestates in the phase shifter circuit 102 and attenuation states in theattenuator circuit 104 by application of digital controls words to therespective circuits, in known manner. As one example, a 5-bit controlword for phase may select one of 32 phase states for the selectablephase shifter circuit 102, and a 4-bit control word for attenuation mayselect one of 16 attenuation states for the selectable attenuatorcircuit 104. A commercial example of a similar circuit is the PE46120Monolithic Phase and Amplitude Controller product from PeregrineSemiconductor Corporation.

Ideal phase shifter circuits provide low insertion loss and equalamplitude (or loss) in all phase states. Ideal phase shifter circuitsalso should operate independent of attenuation, changing only the phaseof an input signal with no effect on insertion loss. However, actualphase shifter circuits have an inherent and unwanted variability ofinsertion loss that depends on the selected phase state. For example,FIG. 2 is a graph of one simulation of a digital phase shifter circuitshowing the variability of insertion loss (in dB, measured relative to atarget value of about −5.8 dB, shown by a dotted line 200) as a functionof phase state selection (each state is designated by a dot on thedashed line 202). The insertion loss variability is due to internalcomponent and path differences within a phase shifter circuit asdifferent phase shifting circuit components are switched in or out ofthe signal path, as well as impedance differences between binarycomponents and/or impedance changes in the aggregate path of the RFsignal.

Similarly, ideal attenuator circuits should operate independent of phaseshifts, changing only the attenuation of an input signal with no effecton phase. However, actual attenuator circuits may cause unwanted phasevariations that depend on the selected attenuation state.

The above problems become particularly acute as the number of stateselection bits and corresponding internal interactions increases.

Accordingly, there is a need for a phase shifter circuit that exhibitslittle or no effect on insertion loss when changing phase state, and amethod for calibrating and selecting phases states for such a circuit.There is also a need for an attenuator circuit that exhibits little orno effect on phase when changing attenuation state, and a method forcalibrating and selecting attenuation states for such a circuit. Thepresent invention addresses these needs.

SUMMARY OF THE INVENTION

The present invention comprises an electronic system that includes adigitally selectable phase shifter circuit and an insertion loss fineadjustment circuit such that the system as a whole exhibits little or noinsertion loss variation when changing phase state, and a method forcalibrating and selecting phases states for such a system. The presentinvention further comprises an electronic system that includes adigitally selectable attenuator circuit and a phase fine adjustmentcircuit such that the system as a whole exhibits little or no effect onphase when changing attenuation state, and a method for calibrating andselecting attenuation states for such a system. Also encompassed withinthe invention is a combination of a digitally selectable phase shiftercircuit, a digitally selectable attenuator circuit, and a fineadjustment circuit that provides selectable state change stabilizationfor either or both of such circuits.

In particular, to minimize insertion loss variability in an electronicsystem that includes a digitally selectable phase shifter circuit, smallselectable attenuators are coupled to the phase shifter circuit.Insertion loss variability between selected phase states is minimized byselectively adding small losses (levels of attenuation) to those phasestates having better insertion loss so as to substantially equalizeinsertion loss across all phases states. Optionally, a bias may beapplied to all phase states so as to make available “negative”attenuation levels, thereby allowing a varying amount of attenuation asneeded to move pre-adjustment phase state insertion losses closer to apost-adjustment insertion loss target value.

Similarly, to minimize phase variability in an electronic system thatincludes a digitally selectable attenuator circuit, small selectablephase shifters are coupled to the attenuator circuit. Phase variabilitybetween selected attenuation states is minimized by selectively addingsmall phase adjustments to attenuation states exhibiting phase shifts soas to substantially equalize phase across all attenuation states.

A calibration process maps each phase and/or attenuation state to adesired level of compensating attenuation or phase (which may be zero insome cases). The compensating phase and attenuation settings for a fineadjustment circuit may be stored in a look-up table (e.g., a read-onlymemory, or a set of settable switches or fuses, or a hard-codedmetallization layer) that encodes such settings as fixed values mappedto corresponding phase state or attenuation state control words. Inaddition, some embodiments of the invention allow the level ofadjustment produced by the fine adjustment circuit to be selectablyprogrammed by a user.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a prior art electronic system that includesa selectable phase shifter circuit coupled to a selectable attenuatorcircuit and an input/output interface block.

FIG. 2 is a graph of one simulation of a phase shifter circuit showingthe variability of insertion loss as a function of phase stateselection.

FIG. 3 is a block diagram showing a phase state adjustment embodiment ofthe invention.

FIG. 4A is a block diagram of one embodiment of a fine adjustmentcircuit.

FIG. 4B is a schematic diagram of an “L-pad” attenuator circuit suitablefor use as an adjustment stage.

FIG. 4C is a schematic diagram of an shunt-switched resistor attenuatorcircuit suitable for use as an adjustment stage.

FIG. 5 is a block diagram of one embodiment of an adjustment controlcircuit.

FIG. 6 shows a first graph of one simulation of a phase shifter circuitshowing the variability of insertion loss as a function of phase stateselection (pre-adjustment), and a second graph of insertion loss as afunction of phase state selection after select amounts of attenuationhave been applied (post-adjustment).

FIG. 7A is a set of graphs for a particular simulation of a phaseshifter circuit showing the pre-adjustment variability of attenuation asa function of phase state selection and frequency, illustrating thedegree of compensation per phase state needed to equalize insertionloss.

FIG. 7B is a set of graphs for the same simulation of a phase shiftercircuit as in FIG. 7A, but showing the post-adjustment variability ofattenuation as a function of phase state selection and frequency,illustrating the degree of compensation per phase state applied toequalize insertion loss.

FIG. 8 is a block diagram showing a more general phase and attenuationadjustment embodiment of the invention.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises an electronic system that includes adigitally selectable phase shifter circuit and an insertion loss fineadjustment circuit such that the system as a whole exhibits little or noeffect on insertion loss when changing phase state, and a method forcalibrating and selecting phases states for such a system.

The present invention further comprises an electronic system thatincludes an attenuator circuit and a phase fine adjustment circuit suchthat the system as a whole exhibits little or no effect on phase whenchanging attenuation state, and a method for calibrating and selectingattenuation states for such a system.

In particular, to minimize insertion loss variability in an electronicsystem that includes a digitally selectable phase shifter circuit, smallselectable attenuators are coupled to the phase shifter circuit.Insertion loss variability between selected phase states is minimized byselectively adding small losses (levels of attenuation) to those phasestates having better insertion loss so as to substantially equalizeinsertion loss across all phase states. Optionally, a bias may beapplied to all phase states so as to make available “negative”attenuation levels, thereby allowing a varying amount of attenuation asneeded to move pre-adjustment phase state insertion losses closer to apost-adjustment insertion loss target value. In some embodiments,variability between selected phase states may be corrected byselectively applying small amounts of gain adjustments rather thanattenuation adjustments; gain adjustments may be thought of as“negative” attenuation adjustments. Further, a combination of gain andattenuation adjustments may be used to correct such phase variability.

Similarly, to minimize phase variability in an electronic system thatincludes a digitally selectable attenuator circuit, small selectablephase shifters are coupled to the attenuator circuit. Phase variabilitybetween selected attenuation states is minimized by selectively addingsmall phase adjustments to attenuation states exhibiting phase shifts soas to substantially equalize phase across all attenuation states.

A calibration process maps each phase and/or attenuation state to adesired level of compensating attenuation or phase (which may be zero insome cases). The compensating phase and attenuation settings for a fineadjustment circuit may be stored in a look-up table (e.g., a read-onlymemory, or a set of settable switches or fuses, or a hard-codedmetallization layer) that encodes such settings as fixed values mappedto corresponding phase state or attenuation state control words. Inaddition, some embodiments of the invention allow the level ofadjustment produced by the fine adjustment circuit to be selectablyprogrammed by a user.

Embodiments of the invention are particularly useful as the number ofstate selection bits and corresponding internal interactions increases.

Phase State Adjustment Embodiment

FIG. 3 is a block diagram showing a phase state adjustment embodiment300 of the invention. In the illustrated embodiment, a selectable phaseshifter circuit 302 is coupled to an RF input signal, RF_In, and theoutput of the selectable phase shifter circuit 302 is coupled to an fineadjustment circuit 304. The output of the fine adjustment circuit 304 iscoupled to a selectable attenuator circuit 306, the output of which isRF_Out, a modified form of the RF_In signal.

The selectable phase shifter circuit 302 and the selectable attenuatorcircuit 306 are both coupled to corresponding control word lines from aninput/output interface 308. The input/output interface 308 serves as aninterface for communication with external circuitry, for example, bymeans of the well-known serial peripheral interface (SPI) serial bus.The phase states and attenuation levels may be specified by externalcircuitry via such a serial interface. The input/output interface 308converts the specified states and levels to control words, conveyed by aphase bus 310 and an attenuation bus 312, for selecting a respectivephase state for the selectable phase shifter circuit 302 and anattenuator state the selectable attenuator circuit 306. The width of thecontrol words (e.g., 4 bits, 5 bits) is a matter of design choice.

The illustrated embodiment also includes an adjustment control circuit314. One input to the illustrated adjustment control circuit 314 is thephase control word from the phase bus 310. In response to a phasecontrol word value, the adjustment control circuit 314 outputs anadjustment control word on a corresponding bus 316 to the fineadjustment circuit 304.

The illustrated fine adjustment circuit 304 is functionally similar tothe selectable attenuator circuit 306, except that the level ofselectable attenuation is very fine. For example, for a 3-bit adjustmentcontrol word that allows selection of any of 8 combinations ofattenuation levels (including zero attenuation), the illustrated fineadjustment circuit 304 may include three stages of fine attenuators:0.05 dB, 0.1 dB, and 0.2 dB (in contrast, a typical selectableattenuator circuit 306 has a minimum attenuation value of about 0.5 dB).It has been found that differences in insertion loss caused by differentselected phase states can generally be compensated by some combinationof such fine values, in general, with an attenuation resolution (i.e.,attenuation step size) of less than about 0.5 dB, and typically lessthan about 0.5 dB of total available adjustment attenuation.

As a more specific example, a 3-bit adjustment control word can bemapped to and control 0.05 dB, 0.1 dB, and 0.2 dB attenuators inaccordance with the following Table 1:

TABLE 1 bit2 bit1 bit0 Total Attenuation 0.2 dB 0.1 dB 0.05 dB Level(dB) 0 0 0 0.0  0 0 1 0.05 0 1 0 0.1  0 1 1 0.15 1 0 0 0.2  1 0 1 0.25 11 0 0.3  1 1 1 0.35

FIG. 4A is a block diagram of one embodiment of a fine adjustmentcircuit 304. Shown are “n” attenuator adjustment stages 330 a-330 ncoupled by corresponding selection lines S₁-S_(n) to an n-bit adjustmentcontrol word conveyed by a corresponding adjustment bus 316. Theinternal structure of the adjustment stages 330 a-330 n is a matter ofdesign choice. For example, FIG. 4B is a schematic diagram of an “L-pad”attenuator circuit 330 suitable for use as an adjustment stage 330 a-330n. The L-pad attenuator circuit 330 basically consists of a switchable(2-state) voltage divider circuit formed by two resistors, R₁ and R₂,connected as shown. To turn the attenuator circuit 330 ON (attenuationmode), bypass switch SW₁ is opened and shunt switch SW₂ is closed inresponse to receipt of a corresponding control signal S or S, resultingin a conventional “L-pad” type attenuator configuration with the inputsignal propagating from an In port to an Out port (the SW₁ and SW₂switches are shown in the attenuation mode configuration). The amount ofattenuation and/or reflection is a function of R₁ and R₂, as is known inthe art. To turn the attenuator circuit 330 OFF, bypass switch SW₁ isclosed and shunt switch SW₂ is opened, shunting the input signal aroundswitch SW₁ and effectively bypassing the attenuator circuit 330.

The attenuation characteristics of an “L-pad” type attenuator are wellknown to those skilled in the art. Other attenuator circuits may also beused, such as a “pi” type attenuator or a “bridged T” type attenuator,and such circuits may include a combination of active and/or passivecomponents. Another method of introducing small amounts of attenuationis to use a shunt-switched resistor. FIG. 4C is a schematic diagram ofan shunt-switched resistor attenuator circuit 332 suitable for use as anadjustment stage. A resistor R₃ and a switch SW₃ are connected as shown.To turn the attenuator circuit 332 ON (attenuation mode), shunt switchSW₃ is closed in response to receipt of a corresponding control signal Swith an “ON” state (e.g., binary 1). To turn the attenuator circuit 332OFF (non-attenuation mode), shunt switch SW₃ is opened in response toreceipt of a corresponding control signal S with an “OFF” state (e.g.,binary 0). As is known in the art, in the attenuation mode, ashunt-switched resistor introduces a small amount of attenuation byessentially dissipating and reflecting a small amount of an inputsignal, thereby causing a small impedance mismatch.

While a binary weighted set of adjustment stages 330 a-330 n is shown inFIG. 4A, other weighting schemes may be used, including a linear“thermometer” type attenuation circuit. In addition, while theadjustment stages 330 a-330 n are shown series connected, equivalentfunctionality can be achieved by switching one or more of “n” parallelattenuators into series between the In and Out ports. Various hybridseries-and-parallel equivalent circuits may also be used so as toselectively switch in a fine adjustment attenuation level into the RFsignal path in order to offset changes in insertion loss as phase statevaries.

In alternative embodiments, variability between selected phase statesmay be corrected by selectively applying small amounts of gainadjustments rather than attenuation adjustments; gain adjustments may bethought of as “negative” attenuation adjustments. Further, a combinationof gain (negative attenuation) and attenuation adjustments may be usedto correct such phase variability. The challenge and trade-off in usinggain adjustments include designing amplifying stages that maintainreasonably linearity and dealing with greater current consumption;nevertheless, use of gain (negative attenuation) adjustments may beuseful for some applications. However, in general, an advantage ofadding positive attenuation (rather than negative attenuation in theform of gain) is less degradation of linearity and lower currentconsumption.

In a simple form, the adjustment control circuit 314 simply maps aninput phase selection control word from the phase bus 310 to anadjustment control word for output to the fine adjustment circuit 304. Acalibration process maps each phase state to a desired level ofcompensating attenuation (which may be zero in some cases). Thecompensating attenuation settings for the insertion loss fine adjustmentcircuit may be stored in a look-up table (e.g., a read-only memory, or aset of settable switches or fuses, or a combinational logic decoderhard-coded by means of a metallization layer) that encodes such settingsas fixed values mapped to corresponding phase state control words. Inaddition, some embodiments of the invention allow the level ofattenuation produced by the insertion loss fine adjustment circuit to beselectably programmed by a user.

FIG. 5 is a block diagram of one embodiment of an adjustment controlcircuit 314. In addition to receiving phase selection control words fromthe input/output interface 308 by means of a corresponding phase bus310, the adjustment control circuit 314 similarly receives phaseselection control words over a direct control bus 320, and also receivesa mode selector signal 322 (a line or bus). The phase bus 310 is coupledto a look-up table 324 that maps particular phase selection controlwords to corresponding adjustment control words conveyed by a mappedadjustment bus 311. The direct control bus 320 conveys adjustmentcontrol words provided by a user's system through the input/outputinterface 308, for example, through dynamically programmed controlcircuitry (not shown) or from an external look-up table. This featuremay be useful when a customer wishes to map phase control words toadjustment control words in a final system configuration to take intoaccount all influences on the selectable phase shifter circuit 302(e.g., adjacent circuitry, ground planes on circuit boards, etc.).

The mode selector signal 322 is coupled to a bus multiplexer 326 andselects either the mapped adjustment bus 311 from the look-up table 324or the direct control bus 320 as the output of the adjustment controlcircuit 314. In some embodiments, the mode selector signal 322 may alsobe coupled (shown with dotted lines) to the look-up table 324 so as toselect one of “N” mappings of phase control words to adjustment controlwords. Thus, for example, if the look-up table 324 comprises multiple“pages” (e.g., 8 pages) of memory locations that map input control wordsto output control words, then different pages can be selected by a modeselector signal 322 of appropriate width (e.g., 3-bits) under externalprogram control. This feature may be useful in a variety of ways; forexample, the behavior of the selectable phase shifter circuit 302 may beknown to vary depending on specific environmental factors (e.g., ambientor circuit temperature, integrated circuit fabrication processvariation), system configuration, or input signal frequency, andaccordingly different mappings of input phase selection control words toadjustment control words may be appropriate at different times or underdifferent conditions.

Phase State Control Word to Adjustment Control Word Mapping

Mapping of phase control words to adjustment control words may be donein several ways, to the same end: selecting an amount of attenuation foreach phase state so that phase states having better insertion loss areattenuated more than phase states have worse insertion loss, in order tosubstantially equalize insertion loss across all phase states.

For example, FIG. 6 shows a first graph 602 of one simulation of a phaseshifter circuit showing the variability of insertion loss as a functionof phase state selection (pre-adjustment), and a second graph 604 ofinsertion loss as a function of phase state selection after selectamounts of attenuation have been applied (post-adjustment). The amountof pre-adjustment insertion loss for phase state 3 (PS3) is less thanthe insertion loss for phase state 15 (PS15). Accordingly, moreattenuation is needed for phase state 3 than for phase state 15 in orderto “flatten” the pre-adjustment graph 602 to be like the post-adjustmentgraph 604.

In general, the amount of attenuation needed for each phase stateselection will vary and may be determined empirically during acalibration stage of component manufacture. For example, an integratedcircuit embodiment of the invention can be tested against differentvalues of adjustment control words at each phase state, and the value ofthe adjustment control word at each phase state that best achieves adesired level of insertion loss may be selected and stored in a look-uptable. One efficient method of testing is to apply a binary searchpattern (also known as a half-interval search algorithm). For a 3-bitadjustment word, only 3 tests need be made to find the best attenuationlevel among the 8 possible states, starting with a middle value. Forexample, referring to Table 1 above, testing could start with a binaryadjustment value of “100” (corresponding to 0.2 dB in this example), andmove up or down the table of values by about one-half of the differencebetween a current value (e.g., “100”) and the next applicable range ofvalues. Thus, if an adjustment value of “100” is too little attenuation,then test the value halfway between “100” and “111” (i.e., “110”); if“110” is too much attenuation, then test the value halfway between “110”and “100” (i.e., “101”).

It should be noted that the insertion loss for some pre-adjustment phasestates may be worse than a desired target value (e.g., about −5.8 dB inthe illustrated example). Hence, in some embodiments, it may bedesirable to apply a “negative” attenuation that lessens the insertionloss for such phase states. This may be accomplished by selecting acombination of the adjustment control word bits that applies a “middle”amount of attenuation (i.e., a bias) to all phase states, therebyallowing a varying amount of attenuation as needed to movepre-adjustment phase state insertion losses closer to a post-adjustmentinsertion loss target value. For example, referring to Table 1 above,all phase states may be initially attenuated by 0.15 dB (adjustmentcontrol word value 011 in this example) so that more or less attenuationcan be applied to adjust the insertion loss occurring at each phasestate closer to a target value. As an alternative, as noted above, smallamounts of gain adjustments may be used to the same end.

FIG. 7A is a set of graphs for a particular simulation of a phaseshifter circuit showing the pre-adjustment variability of attenuation asa function of phase state selection and frequency (graph lines 702 a,704 a, 706 a), illustrating the degree of compensation per phase stateneeded to equalize insertion loss. In this figure (and in FIG. 7Bbelow), insertion loss (in dB) is plotted against individual phasestates 0 to 31, corresponding to respective phase shifts of 2.8° to87.2° in this example. Each graph line 702 a, 704 a, 706 a representingan individual frequency. FIG. 7A illustrates one reason for mappingphase state to multiple “pages” of adjustment control words in thelook-up table 324: different amounts of adjustment attenuation can beapplied as a function of frequency as well as of phase state.

FIG. 7B is a set of graphs for the same simulation of a phase shiftercircuit as in FIG. 7A, but showing the post-adjustment variability ofattenuation as a function of phase state selection and frequency (graphlines 702 b, 704 b, 706 b), illustrating the degree of compensation perphase state applied to equalize insertion loss. The phase states withlower insertion loss are attenuated to flatten overall insertion lossresponse across phase state. While variability of insertion loss acrossall phases states is not eliminated in this example, such variability issubstantially reduced compared to the pre-adjustment graphs lines 702 a,704 a, 706 a shown in FIG. 7A. For example, at 2.5 GHz, the insertionloss across all phase states is within about ±0.05 dB.

Alternative Embodiments & General Adjustment Embodiment

The inventive concepts extend to a number of alternative embodiments.For example, referring to FIG. 3, the serial coupled selectable phaseshifter circuit 302, fine adjustment circuit 304, and selectableattenuator circuit 306 can be rearranged into any serial order. Further,the concept of adding fine adjustments to compensate for insertion lossvariability as a function of phase state extends to functionallycomparable parallel circuit embodiments of the fine adjustment circuit304.

In addition, the embodiments described above have focused on adjustingsignal attenuation to offset variability of insertion loss as a functionof phase state. However, the same concepts can be applied to adjustingsignal phase to offset phase variability as a function of attenuationstate. That is, attenuation state changes applied to the selectableattenuator circuit 306 may result in changes to the phase of an inputsignal as various attenuator circuit components are switched in and outof the signal path from RF_In to RF_Out. Accordingly, fine phaseadjustment circuits controlled by adjustment control word values mappedto attenuation states may be selectively switched into the signal pathto offset such phase variability. The fine phase adjustment circuits mayallow positive and/or negative phase shifts. Such fine phase adjustmentcircuits are a matter of design choice, and may include, for example,one or more inductive components L, capacitive components C, orcombination LC phase shifters, including circuits with a combination ofactive and passive components (such as the digitally tunable capacitorcircuits described in U.S. Pat. No. 9,024,700 B2, entitled “Method andApparatus for Use in Digitally Tuning a Capacitor in an IntegratedCircuit Device”, issued May 5, 2015, and assigned to the assignee of thepresent invention, the teachings of which are hereby incorporated byreference). In general, the amount of phase adjustment needed for eachattenuation state selection will vary and may be determined empiricallyduring a calibration stage of component manufacture, similar to themethod described above for the attenuation fine adjustment circuit 304.However, it is useful to have a fine degree of control over the amountof phase adjustment, and in general the minimum amount of adjustmentresolution (i.e., phase step size) should be less than or equal to about2.8 degrees of phase.

FIG. 8 is a block diagram showing a more general phase and attenuationadjustment embodiment of the invention. A first selectable component802, which may be a selectable phase shifter circuit or a selectableattenuator circuit, is coupled to an RF signal path between RF_In andRF_Out. A second selectable component 806, which may be a selectableattenuator circuit or a selectable phase shifter circuit (but theopposite function of the first selectable component 802) is also coupledto the RF signal path. A fine adjustment circuit 804 is also coupled tothe RF signal path. These three components (802, 804, 806) can berearranged into any serial order, and functionally comparable parallelcircuit embodiments may be substituted.

As in FIG. 3, an input/output interface 308 serves as an interface forcommunication with external circuitry. Busses 810, 812 from theinput/output interface 308 convey state control words to the firstselectable component 802 and the second selectable component 806 (eitherphase or attenuation state control words, as appropriate). Similarly, abus 814 from the input/output interface 308 conveys phase and/orattenuation state control words to an adjustment control circuit 314′,which is also coupled to a mode selector signal line or bus 322.Optionally, a direct control bus 320 may be coupled from theinput/output interface block 308 to the adjustment control circuit 314′.In alternative embodiments, these three components (802, 804, 806) maybe controlled through completely distinct control interfaces and only“joined”, from a control perspective, in software. Thus, there may bemultiple circuit blocks that are controlled separately but give the sameresult.

Similar to the adjustment control circuit 314 of FIG. 3, the adjustmentcontrol circuit 314′ includes a look-up table that maps particular phaseselection control words and/or attenuation selection control words tocorresponding adjustment control words. If present, the direct controlbus 320 conveys adjustment control words provided by a user's systemthrough the input/output interface 308. The mode selector signal line orbus 322 controls whether the adjustment control circuit 314′ outputsmapped adjustment control words or direct adjustment control words.

The fine adjustment circuit 804 receives adjustment control words(mapped or direct) and provides fine tuning of attenuation and/or phaseas a function of phase state and/or attenuation state. While shown asone circuit block, the fine adjustment circuit 804 may be implemented asseparate attenuation adjustment and phase adjustment circuits. Theadjustment control circuit 314′ may be implemented with a single look-uptable coupled to a combined attenuation/phase fine adjustment circuit804 or to separate attenuation adjustment and phase adjustment circuits.Alternatively, the adjustment control circuit 314′ may be implementedwith separate look-up tables for mapping attenuation and phase toadjustment control words, which may be coupled to a combinedattenuation/phase fine adjustment circuit 804 or to separate attenuationadjustment and phase adjustment circuits.

As in the other embodiments described above, mapping of phase controlwords to adjustment control words may be done in several ways, so as toselect an amount of attenuation for each phase state in order tosubstantially equalize insertion loss across all phase states.Similarly, mapping of attenuation control words to adjustment controlwords may be done in several ways, so as to select an amount of phaseadjustment for each attenuation state in order to substantially equalizephase across all attenuation states.

In some embodiments, there may be a need to “skip” unwanted states thatfor some reason cannot be corrected by fine adjustment (e.g., out ofrange). Accordingly, for such states, no adjustment is made by the fineadjustment circuit 304. This may be accomplished, for example, byappropriate programing of the look-up table 324 in the adjustmentcontrol circuit 314, or by addition of mapping state logic to theadjustment control circuit 314. In doing so, a particular phase orattenuation state would have a relatively increased shift of attenuationor phase (respectively). However, phase monotonicity would be maintainedas well as insertion loss or phase flatness, which may be paramount toan application. Such a feature embedded in the adjustment circuitryautomates the action and avoids external user programming at the macrosystem level. The additional complexity is that the adjustment controlcircuit 314 would play a role in affecting other states.

Methods

Another aspect of the invention includes a method for compensating forvariations in insertion loss as phase state changes in a selectablephase shifter circuit, including selecting and applying an amount ofattenuation for each phase state so that phase states having betterinsertion loss are attenuated more than phase states that have worseinsertion loss, in order to substantially equalize insertion loss acrossall phases states.

Another aspect of the above method includes applying a bias level ofattenuation to all phase states and selecting an amount of adjustmentattenuation for each phase state so as to move pre-adjustment phasestate insertion losses closer to a post-adjustment insertion loss targetvalue.

Yet another aspect of the invention includes a method for compensatingfor variations in phase as attenuation state changes in a selectableattenuator circuit, including selecting and applying an amount of phaseshift for each attenuation state in order to substantially equalizephase shift across all attenuation states.

Additional aspects of the above methods include storing adjustmentvalues in a look-up table that maps applied phase and/or attenuationcontrol words to adjustment control words; selectably outputting eithermapped adjustment control words or externally-supplied adjustmentcontrol words to a fine adjustment circuit that provides fine adjustmentof phase and/or attenuation to an applied RF signal; selectingadjustment control words for storing by empirically comparing levels ofattenuation or phase shift for each phase state or attenuation state,and storing the adjustment control word for each such state that bestachieves a desired level of insertion loss or phase; and selecting andmapping adjustment control words by means of a binary search pattern.

Implementation

As should be readily apparent to one of ordinary skill in the art,various embodiments of the invention can be implemented to meet a widevariety of specifications. Thus, selection of suitable component valuesare a matter of design choice. Various embodiments of the invention maybe implemented in any suitable integrated circuit (IC) technology(including but not limited to MOSFET and IGFET structures), or in hybridor discrete circuit forms. Integrated circuit embodiments may befabricated using any suitable substrates and processes, including butnot limited to standard bulk silicon, silicon-on-insulator (SOI),silicon-on-sapphire (SOS), GaAs pHEMT, and MESFET processes. Voltagelevels may be adjusted or voltage polarities reversed depending on aparticular specification and/or implementing technology (e.g., NMOS,PMOS, or CMOS). Component voltage, current, and power handlingcapabilities may be adapted as needed, for example, by adjusting devicesizes, “stacking” components to handle greater voltages, and/or usingmultiple components in parallel to handle greater currents.

A number of embodiments of the invention have been described. It is tobe understood that various modifications may be made without departingfrom the spirit and scope of the invention. For example, some of thesteps and circuits described above may be order independent, and thuscan be performed or arranged in an order different from that described.Various activities described with respect to the methods identifiedabove can be executed in repetitive, serial, or parallel fashion. It isto be understood that the foregoing description is intended toillustrate and not to limit the scope of the invention, which is definedby the scope of the following claims, and that other embodiments arewithin the scope of the claims.

What is claimed is:
 1. An electronic circuit for modifying an appliedradio frequency, including: (a) at least one of (1) a phase shiftercircuit for modifying the phase of the applied radio frequency signal inresponse to applied phase state digital control words, and (2) anattenuator circuit for selectively attenuating the applied radiofrequency signal in response to applied attenuation state digitalcontrol words; and (b) a fine adjustment circuit coupled to at least oneof the phase shifter circuit and the attenuator circuit, the fineadjustment circuit including at least one of (1) an adjustmentattenuator circuit for providing selectable attenuation as a function ofthe applied phase state digital control words to substantially equalizeinsertion loss variations between phase states selected by the appliedphase state digital control words, and (2) an adjustment phase shiftercircuit for providing a selectable phase shift adjustment as a functionof the applied attenuation state digital control words to substantiallyequalize phase variations between attenuation states selected by theapplied attenuation digital control words.
 2. A radio frequencyelectronic circuit, including: (a) a phase shifter circuit for modifyingthe phase of an applied radio frequency signal in response to appliedphase state digital control words; and (b) a fine adjustment circuitseries coupled to the phase shifter circuit, the fine adjustment circuitincluding a plurality of selectable attenuator circuits for providingselectable attenuation of the phase-modified applied radio frequencysignal as a function of the applied phase state digital control words tosubstantially equalize insertion loss variations between phase statesselected by the applied phase state digital control words.
 3. The radiofrequency electronic circuit of claim 2, wherein the attenuation of theplurality of selectable attenuator circuits is selected by adjustmentdigital control words applied to the fine adjustment circuit.
 4. Theradio frequency electronic circuit of claim 3, further including anadjustment control circuit coupled to the fine adjustment circuit forapplying adjustment digital control words to the fine adjustmentcircuit.
 5. The radio frequency electronic circuit of claim 4, whereinthe adjustment control circuit includes a look-up table that maps theapplied phase state digital control words to at least one set ofadjustment digital control words.
 6. The radio frequency electroniccircuit of claim 5, wherein the adjustment control circuit is coupled toan external source of adjustment digital control words, and furtherincludes a multiplexer for selectably applying adjustment digitalcontrol words to the fine adjustment circuit from one of the look-uptable or the external source of adjustment digital control words.
 7. Theradio frequency electronic circuit of claim 2, wherein providingselectable attenuation to substantially equalize insertion lossvariations between phase states selected by the applied phase statedigital control words includes applying a level of attenuation to thosephase states having better insertion loss that is greater than the levelof attenuation applied to those phase states having worse insertionloss.
 8. The radio frequency electronic circuit of claim 2, wherein thestep size of the attenuation provided by the plurality of selectableattenuator circuits is less than about 0.5 dB.
 9. The radio frequencyelectronic circuit of claim 2, wherein the plurality of selectableattenuator circuits are series connected.
 10. A digitally-controlledradio frequency electronic circuit, including: (a) an attenuator circuitfor selectively attenuating an applied radio frequency signal inresponse to applied attenuation state digital control words; and (b) afine adjustment circuit series coupled to the attenuator circuit, thefine adjustment circuit including a plurality of selectable phaseshifter circuits for providing a selectable phase shift adjustment ofthe attenuated applied radio frequency signal as a function of theapplied attenuation state digital control words to substantiallyequalize phase variations between attenuation states selected by theapplied attenuation digital control words.
 11. The radio frequencyelectronic circuit of claim 10, wherein the phase shift adjustment ofthe plurality of selectable phase shifter circuits is selected byadjustment digital control words applied to the fine adjustment circuit.12. The radio frequency electronic circuit of claim 11, furtherincluding an adjustment control circuit coupled to the fine adjustmentcircuit for applying adjustment digital control words to the fineadjustment circuit.
 13. The radio frequency electronic circuit of claim12, wherein the adjustment control circuit includes a look-up table thatmaps the applied attenuation state digital control words to at least oneset of adjustment digital control words.
 14. The radio frequencyelectronic circuit of claim 13, wherein the adjustment control circuitis coupled to an external source of adjustment digital control words,and further includes a multiplexer for selectably applying adjustmentdigital control words to the fine adjustment circuit from one of thelook-up table or the external source of adjustment digital controlwords.
 15. The radio frequency electronic circuit of claim 10, whereinthe step size of the phase shift provided by the plurality of selectablephase shifter circuits is less than or equal to about 2.5 degrees ofphase.
 16. A digitally-controlled radio frequency electronic circuit,including: (a) a phase shifter circuit for modifying the phase of anapplied radio frequency signal in response to applied phase statedigital control words; and (b) a fine adjustment circuit series coupledto the phase shifter circuit, the fine adjustment circuit including aplurality of selectable attenuator circuits for providing attenuation ofthe phase-modified applied radio frequency signal as a function of theapplied phase state digital control words to substantially equalizeinsertion loss variations between phase states selected by the appliedphase state digital control words; wherein providing attenuation tosubstantially equalize insertion loss variations between phase statesselected by the applied phase state digital control words includesapplying a level of attenuation to those phase states having betterinsertion loss that is greater than the level of attenuation applied tothose phase states having worse insertion loss.
 17. The radio frequencyelectronic circuit of claim 16, wherein the step size of the attenuationprovided by the plurality of selectable attenuator circuits is less thanabout 0.5 dB.
 18. An electronic circuit for modifying an applied radiofrequency, including: (a) at least one of (1) a phase shifter circuitfor modifying the phase of the applied radio frequency signal inresponse to applied phase state digital control words, and (2) anattenuator circuit for selectively attenuating the applied radiofrequency signal in response to applied attenuation state digitalcontrol words; and (b) a fine adjustment circuit series coupled to atleast one of the phase shifter circuit and the attenuator circuit, thefine adjustment circuit including at least one of (1) a plurality ofselectable adjustment attenuator circuits for providing selectableattenuation adjustment of the phase-modified applied radio frequencysignal as a function of the applied phase state digital control words tosubstantially equalize insertion loss variations between phase statesselected by the applied phase state digital control words, and (2) aplurality of selectable adjustment phase shifter circuits for providinga selectable phase shift adjustment of the attenuated applied radiofrequency signal as a function of the applied attenuation state digitalcontrol words to substantially equalize phase variations betweenattenuation states selected by the applied attenuation digital controlwords.
 19. The electronic circuit of claim 18, wherein the selectableattenuation adjustment or selectable phase shift adjustment provided bythe fine adjustment circuit is selected by adjustment digital controlwords applied to the fine adjustment circuit.
 20. The electronic circuitof claim 19, further including an adjustment control circuit coupled tothe fine adjustment circuit for applying adjustment digital controlwords to the fine adjustment circuit.
 21. The electronic circuit ofclaim 20, wherein the adjustment control circuit includes a look-uptable that maps at least one of the applied phase state digital controlwords or the applied attenuation state digital control words to at leastone set of adjustment digital control words.
 22. The electronic circuitof claim 21, wherein the adjustment control circuit is coupled to anexternal source of adjustment digital control words, and furtherincludes a multiplexer for selectably applying adjustment digitalcontrol words to the fine adjustment circuit from one of the look-uptable or the external source of adjustment digital control words. 23.The electronic circuit of claim 18, wherein providing selectableattenuation adjustment to substantially equalize insertion lossvariations between phase states selected by the applied phase statedigital control words includes applying a level of attenuation to thosephase states having better insertion loss that is greater than the levelof attenuation applied to those phase states having worse insertionloss.
 24. The electronic circuit of claim 18, wherein the step size ofthe attenuation provided by the plurality of selectable adjustmentattenuator circuits is less than about 0.5 dB.
 25. The radio frequencyelectronic circuit of claim 18, wherein the step size of the phase shiftprovided by the plurality of selectable adjustment phase shiftercircuits is less than or equal to about 2.5 degrees of phase.
 26. Amethod of modifying the phase of an applied radio frequency signal,including: (a) modifying the phase of the applied radio frequency signalin response to applied phase state digital control words; and (b)selectably attenuating the modified radio frequency signal by means of aplurality of selectable attenuator circuits as a function of the appliedphase state digital control words to substantially equalize insertionloss variations between phase states selected by the applied phase statedigital control words.
 27. A method for compensating for variations ininsertion loss as phase state changes in a selectable phase shiftercircuit, including selecting and applying an amount of attenuation bymeans of a plurality of selectable attenuator circuits for each phasestate as a function of such phase state so that phase states havingbetter insertion loss are attenuated more than phase states having worseinsertion loss, in order to substantially equalize insertion loss acrossall phase states.
 28. The method of claim 27, further includingselecting the amount of attenuation by applying adjustment digitalcontrol words.
 29. The method of claim 28, further including storingselected adjustment digital control words in a look-up table that mapsphase states to adjustment digital control words.
 30. The method ofclaim 29, further including selecting adjustment digital control wordsfor storing by empirically comparing levels of attenuation correspondingto adjustment digital control words to the insertion loss of theselectable phase shifter circuit for each phase state, and storing theadjustment control word for each phase state that best achieves adesired level of insertion loss.
 31. The method of claim 30, whereincomparing levels of attenuation includes applying levels of attenuationcorresponding to adjustment digital control words in a binary searchpattern.
 32. The method of claim 29, further including selectablyoutputting either mapped adjustment digital control words from thelook-up table or externally-supplied adjustment digital control words asthe applied adjustment digital control words.
 33. The method of claim27, further including applying a bias level of attenuation to all phasestates and selecting an amount of adjustment attenuation for each phasestate so as to move pre-adjustment phase state insertion losses closerto a post-adjustment insertion loss target value.
 34. A method forcompensating for variations in phase as attenuation state changes in aselectable attenuator circuit, including selecting and applying anamount of phase shift by means of a plurality of selectable phaseshifter circuits for each attenuation state by applying adjustmentdigital control words as a function of such attenuation state in orderto substantially equalize phase across all attenuation states.
 35. Themethod of claim 34, further including storing selected adjustmentdigital control words in a look-up table that maps attenuation states toadjustment digital control words.
 36. The method of claim 35, furtherincluding selecting adjustment digital control words for storing byempirically comparing degrees of phase shift corresponding to adjustmentdigital control words to the phase shift of the selectable attenuatorcircuit for each attenuation state, and storing the adjustment controlword for each attenuation state that best achieves a desired degree ofphase.
 37. The method of claim 36, wherein comparing degrees of phaseincludes applying degrees of phase shift corresponding to adjustmentdigital control words in a binary search pattern.
 38. The method ofclaim 35, further including selectably outputting either mappedadjustment digital control words from the look-up table orexternally-supplied adjustment digital control words as the appliedadjustment digital control words.
 39. An electronic circuit formodifying an applied radio frequency, including: (a) a phase shiftercircuit for modifying the phase of the applied radio frequency signal inresponse to applied phase state digital control words; (b) a fineadjustment circuit series coupled to the phase shifter circuit, the fineadjustment circuit including a plurality of selectable adjustmentattenuator circuits for providing selectable attenuation of thephase-modified applied radio frequency signal as a function of theapplied phase state digital control words to substantially equalizeinsertion loss variations between phase states selected by the appliedphase state digital control words; and (c) an attenuator circuit,coupled to the fine adjustment circuit, for selectively attenuating theapplied radio frequency signal in response to applied attenuation statedigital control words.
 40. An electronic circuit for modifying anapplied radio frequency, including: (a) an attenuator circuit forselectively attenuating the applied radio frequency signal in responseto applied attenuation state digital control words; (b) a fineadjustment circuit series coupled to the attenuator circuit, the fineadjustment circuit including a plurality of selectable adjustment phaseshifter circuits for providing a selectable phase shift adjustment ofthe attenuated applied radio frequency signal as a function of theapplied attenuation state digital control words to substantiallyequalize phase variations between attenuation states selected by theapplied attenuation digital control words; and (c) a phase shiftercircuit, coupled to the fine adjustment circuit, for modifying the phaseof the applied radio frequency signal in response to applied phase statedigital control words.